help with cyclones

[Rknott2007]

I am in the process of finishing off my cyclone extraction unit I have received a 55 gallon drum from a work mate and was wondering if other cyclone users have lined their bins or drums with waste sacks, and how to avoid the bag sucking up through the inlet. I dont really want to have to take the drum out to empty as the reason i decided on a cyclone is to save on space so the drum is tucked into the corner of the workshop.

Thanks in advance
Rob

 

[ondablade]

Hi Rob. I'm mid Pentz cyclone install and also have a couple of reconditioned 55 gal drums with ring clamped removable lids for chip collection - and am also thinking of how to secure drum lining bags against the suction generated by the fan.

I've not tried either yet, but I've seen at least two alternative methods reported. You'd need to proceed carefully though, as there's no guarantee that either works:

1. An open ended ring rolled from say 6 - 8mm steel rod to a diameter a little larger than the drum. This is sprung inwards (it could have handles pointing upwards on the ends) slipped down inside the bag while it's empty. You're then supposed to reach down through the chips to remove it before lifting out the bag.

This doesn't sound either convenient or clean to me - you'd need to be outside when removing the ring or it would really mess the shop up....

2. Rather more elegant is the suggestion to take a tapping through say a small bore PVC or metal tube from the centre pipe in the cyclone from just under where it enters the fan - bringing it out through the largely dead zone just under the 'roof'/top of the cyclone. Run a flex tube from this to connect to a barbed stub/short tube mounted in the wall near the bottom of the ship drum. This means that when the fan starts it should suck the air from the space between the bag and the drum wall.

The idea is that with leakage and friction losses that the suction through the tube will deliver marginally lower pressure outside the bag than is inside. Hopefully it works - although the tube would need to be big enough so that the 'suck' arrived outside the bag as quickly as inside after start up, and it's not a certainty that there would be enough negative pressure to hold the bag down. I've seen this version suggested on the Clear Vue forum, but not seen anybody report actually putting it to the test.

Oneida offer a system called a Bag Gripper which seems to use a tube like the above, but possibly with a small vacuum pump???? Search on http://www.oneida-air.com They're notably reluctant to show details, and it's quite expensive.

Whatever the plan it'd be important the bag was always clamped under the bin lid so that if it ever did get sucked up it wouldn't make it right up into the fan.

PS (added later) It'd be nice to get the bag solution going, but one plan B option is the second chip drum I bought - that way I can haul one away to the dump with a blank lid on it while the other takes over. Reconditioned (shot blasted and repainted) 55gal and smaller drums are fairly cheaply available from recyclers.

 

[Bluekingfisher]

I read an article from a US mag where the user had the same problems. What he did was cut a lenght of fairly heavy gauge weldmesh, the type used for fencing to the height of his drum and long enough to roll into a cylinder then tied the ends together with heavy gaude wire to stop the mesh from unrolling. He said it worked for him.

Let me know how it goes, I was going to give it a go on my system when I get it up and running.

David

 

[Rknott2007]

I think I'll try that wire mesh method, seems as though it should work, a bit like the cage on a cam vac I'm assuming.
Another problem is duct sizing. I have 110 plastic soil pipe at the moment and want to upgrade to spiral ducting, my question is should i use 6inch or 5inch, the blower for my cyclone is off the 2hp fox extractor (F50 - 842).

Many thanks
Rob

 

[ondablade]

Ta David, it'll be interesting to hear what comes up. I've since seen a variation like the one you describe reported as working well - only using a sheet of plastic to keep the bag expanded instead of the mesh. The major disadvantage of this or a cage seems to be the need to burrow down into the full bag to remove it - lots of fine dust is potentially put into the air.

I also since put the question up on the US Felder owner group's site and more or less the same options came up - the vacuum tube and the bag support. Nobody could report having actually run the vacuum tube method yet though.

There's a few more issues that did pop up;

1. Whatever size your drum you need a source of cheap and right sized good heavy gauge bags to suit. I've not looked for any to suit my 55 gal drums yet.

2. I'm guessing that on drums with ring/band clamped lids that you would drape the bag over the lip before clamping the lid down. The lid and bag size would need to be able to accommodate this (no big puckers), and at the same time give a good seal as even fairly minor leakage into the drum meses up cyclone function.

3. Removing a full and potentially well packed bag of chips from a drum needs a means of allowing air to bleed into the bottom of the drum under the bag so that removing it doesn't require overcoming the effect of the vacuum which may otherwise form. Fitting a vacuum tube to the bottom of the drum would open up some options in this regard, but it might need to have a decent bore.

4. Overfilling the drum can result in loads of chips being sucked up through the cyclone and through the fan into your nice HEPA filters - the fabric of which is fairly easily damaged - not a desirable state of affairs. So a reliable method of knowing when max level has been reached is a good move. There's commercial level sensor kits about, but maybe a clear bag and viewing window in the side of the drum is an alternative?

 

[ondablade]

I can't really say Rob, as the duct size you need depends on it's length, machine hood restrictions, duct bends/restrictions etc. - i.e. on the total resistance/pressure drop your total system is producing at a given size. Also on whether the fan has a real 2hp, and a fairly optimum impeller fitted.

The second multicolour table well down this page gives a fair estimation of the airflow/duct size/duct length though for a given fan HP and impeller size though: http://www.billpentz.com/woodworking/cy ... Basics.cfm It looks like the larger size should be OK provided the pressure drop is low. (i.e. 4 or 5 in WG)

What's fairly clear is that at 2hp you should probably be trying to keep the length of your duct runs good and short (i.e. place the fan beside the machine), and laid out to be nice and clean flowing - or you risk dropping down to air speeds which are marginal for effective chip and dust collection and transportation.....

 

[yetloh]

It must surely be possible to arrange for the drum to have a static charge which would attract the bag and hold it firmly against the drum walls. I haven't the faintest idea how one might go about this but it would be an elegant solution if it couls be made to work without risk of a dust explosion.

Jim

 

[Rknott2007]

Hmm, what about drilling a small hole into the drum and attaching one a ventri system off a compressor? Like on my vacuum press? Surely this should create enough of a vacuum to hold the bag down?

 

[9fingers]

My cyclone uses a much smaller waste drum ( about 60 litres?) so I dont use a bag. However the only way a bag will get sucked up into the cyclone is if there is a leak in the lower drum. Fit a good seal, and there should be no problem as the pressure (or lack of it) either side of the bag will be similar - I think (caveat!)
Next time I empty mine I'll try and remember to try a bag in it
Bob

 

[Rknott2007]

I'll try it with just a bag once it is all set up, the clearvue forum suggests taking the pipe from the cyclone inlet? Seems simple enough. I'll try all of them a see which is best.

 

[ondablade]

That'd probably be the fan inlet Rob, although you see various suggestions about. In the end I guess you're probably looking for somewhere at lower pressure than the top of the drum where the chips drop in - and hoping there aren't transient changes in this that cause problems...

 

[9fingers]

I tried a bag inside the collection bin of my cyclone yesterday and it works fine. Looking at the clear pipe I have between bin and cyclone, I can see there in no tendency to suck it up into the cyclone at all.

hth

Bob

 

[Rknott2007]

Thanks for checking bob, I guess alot of people have leaks in their drums or bins else there wouldn't be all the info on bag grippers.